Aluminum alloy



Patented June 4, 1935 UNITED STATES PATENT OFFICE 2,003,297 ALUMINUM ALLOY Pennsylvania No Drawing. Application August 29, 1934, Serial No. 742,006

Claims.

This invention relates to an improvement in aluminum base alloys that are not subjected to thermal treatment for the purpose of improving their physical properties.

5 Early in the art or using aluminum it was discovered that the pure metal in and of itself was poorly adapted to many purposes because of its low strength even in the cold worked condition.

In consequence of the demand for a material that would possess the lightness of aluminum and yet have a strength approaching that of steel, aluminum base alloys were developed which had to be heat treated and aged in order to obtain their maximum strength. An aluminum base alloy of the so-called duralumin type containing 4 per cent copper, 0.5 per cent magnesium and 0.5 per cent manganese is a well known representative of this class of wrought heat'treated alloys. In order to attain the maximum strength in such 29 alloys it is necessary to hold them at a temperature of about 510 C. for a short period of time and then quickly cool the metal to a much lower temperature, usually atmospheric or room temperature. The alloy may then be allowed to reas main at ordinary temperatures for a few days, or be heated to a slightly elevated temperature for several hours to assist aging. Alloys treated in this manner are generally less resistant to corrosive attack than the non-heat treated alloys.

30 The decrease in'corrosion resistance is of particular importance where the alloy is exposed t salt water or a salt water atmosphere.

While heat treated alloys of this nature possess a higher strength than the non-heat treated compositions, the heat treating operation adds to the cost of making the final product as well as imposing certain limitations on the design of the article because of warpage that may occur on suddenly cooling from an elevated temperature. Furthermore, non-heat treated alloys may be welded without substantial loss in physical properties in the vicinity of the welded joint whereas heat treated alloys under similar conditions sufier a decrease in strength because of the efiect of the welding heat upon the structure of the alloy. A need has therefore been felt for a cheaper yet strong alloy that would not require heat treatment to develop high physical properties.

One of the objects of our invention, therefore,

is to provi" analloy that will attain a high strength without recourse to special thermal treatment. Another object is to provide an alloy that does not age upon standing at ordinary or slightly elevated temperatures after having been quickly cooled from the annealing temperature.' A further object is to obtain a high strength in an alloy without suffering a loss in corrosion resistance.

We have discovered that the addition to aluminum of from about 0.1 to 3.5 percent magnesium, 0.05 to 0.45 per cent copper, 0.1 to 1.0 per cent manganese, and 0.1 to 0.5 percent chromium, produces an alloy having higher mechanical properties than other non-heat treated alloys under similar conditions of cold working or annealing. The alloy has unusually high tensile, and yield strengths even in the annealed condition as compared tothe common alloys heretofore known and used. The elongation values also are high as compared, with other alloys of comparable strength. Furthermore, these properties remain substantially unchanged upon repeated heating and cooling cycles, which is contrary to the behavior of alloys receivingheat'treatment to develop their full strength. This unique action of our alloy under the influence of repeated heating, and cooling, is attributable, we believe to' the virtually complete solution of the magnesium and copper in the aluminum both at ordinary and elevated temperatures. Unlike the usual heat treated alloys, our composition does not yield a super-saturated solid solution when cooled to room temperatures from a. temperature of say 510 C. Remaining at room temperature for several days, or reheating to slightly higher temperatures, does not cause precipitation or other alteration in the internal structure of the alloy. The solution of magnesium and copper also serves a useful purpose in-strengthening the alloy since the atoms of these elements are more intimately associated with those of aluminum in a state of solid solution than if they remain undissolved. Solid solutions in general exhibit a greater strength than the pure metals of which they are composed- Solid solutions usually develop a coarse grained structure when annealed after being cold worked. We have therefore found it necessary to add both manganese and chromium toour alloy to insure a small uniform grain size. These elements are 2 practically insoluble in aluminum and do not in any way interfere with the behavior of magnesium and copper.

The improvedcharacter of our alloy composition may be most readily demonstrated through comparison with the properties of well known non-heat treated aluminum base alloys. The

alloys under conditions which ordinarily cause an increase in strength of heat treatable alloys is illustrated in the following tables. The specimens of the first group were heated at 950 F. for 15 minutes and quenchedwhile those in the second group were given the same initial treatment plus aging by reheating to 320 F. for 18 composition of the alloys tested is given in the hours. table below, alloys A, B and C being made in ac- Heat treated alloys cordance with our invention while alloys D, E and 10 represent common nonheat treated alloys Tensile Yield which have been widely used. mm memes flegesntini" Per cent alloy composition u r Lbs mm m Alloy Ma M 01! Cr i v A 89,100 mm as s 20,300 10,000 21.: 3.11 0.50 0.41 0.20 o H1500 0.00 0.52 0.21 0.20 5 Heat treated and aged alloys 1.0 1.20 M 41,100 21,000 21.1 1 .000 mm as The alloys were fabricated to sheet form ac- 18.000

cording to the usual hot and cold rolling practices with the necessary intermediate annealing treatment. Specimens were then tested in the full hard or cold rolled and the annealed conditions. In the latter case, the hard rolled stock was annealed at about 7'75 1'. to remove all workingcondition over the common alloys will be seen from the comparative values in the following table of physical properties. 1

- Annealed sheet Tensile Yield strength strength momma 1 per cent in 2" Lbs. per sq. in.

500 1 800 22. 2 700 13:0) 21. 8 29, 500 11, 000 l0. 1 it, 000 s, 000 40. 0 as, 000 I 10,000 20. o 10, 000 5, 000 40. 0

The alloys A, B and C show a marked increase in strength above alloys D, E and F while retaining a satisfactory elongation. Alloy E which has heretofore. been regarded as oneof the strongest non-heat treated alloys falls considerably below the tensile and yield strengths of A and 13.

Further evidence of the improved character of our alloys is seen in the physical properties of the hard rolled material. The following table affords comparison between our alloys and those which have been in common use.

Hard rrolled allow;

measure of the physical'properties 01-0111- B'rom these results and those obtained from the annealed alloys, it is apparent that there is but little variation in strength of the heated product. The data further discloses the fact that under aging conditions there was scarcely any variation in strength which is interpreted to mean that all of the constituents soluble at an 7 elevated temperature remain in solution at ordinary or slightly elevated temperatures.

The improved 'corromon resistance of our alloys may beshown by the results of an exposure to a severe test consisting of alternately immersing in and elevating the test specimens from an aqueous solution of 5.26 per cent sodium chloride and 0.3 per cent hydrogen peroxide. Samples of a well known heat treated, quenched and naturally aged aluminum base alloy containing about 4 per. cent copper, 0.5 per cent magnesium and 0.5 per cent manganese were tested along with annealed samples of alloys 11,13 and O. The heat treated alloy was exposed for only 24 hours while the other alloys were subjected to the test for another 24 hours, making a total of 48 hours continuous exposure. The losses in physical properties compared to the original properties of the uncorroded alloys are expressed in terms of per-.

centage decrease in the table below. Per cent loss in physical properties of corroded The foregoing advantageous properties are exhibited over a range of from about 0.1 to 8.5 per 4 cent magnesium, 0.1 to 0.45 per cent copper, 0.1 to 1 per cent manganese and 0.1 to 0.5 per cent chromium. If exceptional ease in working is desired, but not maximum strength. a small total amount of alloying ingredients will suffice. However, for general purposes we prefer to use from about 1.5 to '3 per cent magnesium, 0.2 to 0.4 per cent copper, 0.4 to 0.8 per cent manganese V and 0.15 to 0.4 per cent chromium. The magnesium and copper must in any case be kept below the maximum solid solubility at room temperature, hence the upper limit for um is set at 3.5 per cent and copper at 0.45 per cent. To obtain the best results and yet have a readily workable alloy, we have found it n to limit the iron and silicon impurity content of aluminum to a total maximum 01 about 0.3 per cent, although under certain conditions as much as 0.5 per cent may be allowed. The term aluminum as used herein refers to the grade or metal containing not more than about 0.5 per cent total impurities.

We claim:

1. An aluminum base alloy comprising from about 0.1 to 3.5 per cent magnesium, 0.1 to 0.45 per cent copper, 0.1 to 1 per cent manganese and 0.1 to 0.5 per cent chromium-the balance being aluminum. i

2. An aluminum base alloy comprising from about 1.5 to 3 per cent magnesium, 0.2'to 0.4 per cent copper, 0.4 to 0.8 per cent manganese, and 0.15 to 0.4 per cent chromium, the balance being aluminum.

3. An aluminum base alloy composed oi! about 3 per cent magnesium, 0.4 per cent copper, 0.5 per cent manganese and 0.25 per cent chromium, the balance being aluminum.

4. An aluminum base alloy composed of about 3 per cent magnesium, 0.2 per cent copper, 0.5 per cent manganese, and 025 per cent chromium. the balance being aluminum.

5. An aluminum base alloy composed of about 1.4 per cent magnesium, 0.5 per cent manganese,

0.4 per cent copper and 0.25 per cent chromium, the balance being aluminum.

FRED KELLER. RICHARD S. MERRITI. 

